937 research outputs found
Electron spin relaxation can enhance the performance of a cryptochrome-based magnetic compass sensor
The radical pair model of the avian magnetoreceptor relies on longâlived electron spin coherence. Dephasing, resulting from interactions of the spins with their fluctuating environment, is generally assumed to degrade the sensitivity of this compass to the direction of the Earth's magnetic field. Here we argue that certain spin relaxation mechanisms can enhance its performance. We focus on the flavinâtryptophan radical pair in cryptochrome, currently the only candidate magnetoreceptor molecule. Correlation functions for fluctuations in the distance between the two radicals in Arabidopsis thaliana cryptochrome 1 were obtained from molecular dynamics simulations and used to calculate the spin relaxation caused by modulation of the exchange and dipolar interactions. We find that intermediate spin relaxation rates afford substantial enhancements in the sensitivity of the reaction yields to an Earthâstrength magnetic field. Supported by calculations using toy radical pair models, we argue that these enhancements could be consistent with the molecular dynamics and magnetic interactions in avian cryptochromes
Implementation of NMR quantum computation with para-hydrogen derived high purity quantum states
We demonstrate the first implementation of a quantum algorithm on a liquid
state nuclear magnetic resonance (NMR) quantum computer using almost pure
states. This was achieved using a two qubit device where the initial state is
an almost pure singlet nuclear spin state of a pair of 1H nuclei arising from a
chemical reaction involving para-hydrogen. We have implemented Deutsch's
algorithm for distinguishing between constant and balanced functions with a
single query.Comment: 7 pages RevTex including 6 figures. Figures 4-6 are low quality to
save space. Submitted to Phys Rev
No evidence for magnetic field effects on the behaviour of Drosophila
Migratory songbirds have the remarkable ability to extract directional information from the Earthâs magnetic field1,2. The exact mechanism of this light-dependent magnetic compass sense, however, is not fully understood. The most promising hypothesis focuses on the quantum spin dynamics of transient radical pairs formed in cryptochrome proteins in the retina3,4,5. Frustratingly, much of the supporting evidence for this theory is circumstantial, largely because of the extreme challenges posed by genetic modification of wild birds. Drosophila has therefore been recruited as a model organism, and several influential reports of cryptochrome-mediated magnetic field effects on fly behaviour have been widely interpreted as support for a radical pair-based mechanism in birds6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23. Here we report the results of an extensive study testing magnetic field effects on 97,658âflies moving in a two-arm maze and on 10,960âflies performing the spontaneous escape behaviour known as negative geotaxis. Under meticulously controlled conditions and with vast sample sizes, we have been unable to find evidence for magnetically sensitive behaviour in Drosophila. Moreover, after reassessment of the statistical approaches and sample sizes used in the studies that we tried to replicate, we suggest that manyâif not allâof the original results were false positives. Our findings therefore cast considerable doubt on the existence of magnetic sensing in Drosophila and thus strongly suggest that night-migratory songbirds remain the organism of choice for elucidating the mechanism of light-dependent magnetoreception
Pollution Potential of Cattle Feedlots and Manure Storages in the Canadian Great Lakes Basin: Agricultural Watershed Studies, Project 21: Final Report
Condensation of charged bosons in plasma physics and cosmology
The screening of impurities in plasma with Bose-Einstein condensate of
electrically charged bosons is considered. It is shown that the screened
potential is drastically different from the usual Debye one. The polarization
operator of photons in plasma acquires infrared singular terms at small photon
momentum and the screened potential drops down as a power of distance and even
has an oscillating behavior, similar to the Friedel oscillations in plasma with
degenerate fermions. The magnetic properties of the cosmological plasma with
condensed W-bosons are also discussed. It is shown that W-bosons condense in
the ferromagnetic state. It could lead to spontaneous magnetization of the
primeval plasma. The created magnetic fields may seed galactic and
intergalactic magnetic fields observed in the present-day universe.Comment: 9 pages, invited talk at the International Seminar "Quarks 2010",
Kolomna, Russia, June, 6-12, 201
Bird Cryptochrome 1a Is Excited by Blue Light and Forms Long-Lived Radical- Pairs
Cryptochromes (Cry) have been suggested to form the basis of light-dependent
magnetic compass orientation in birds. However, to function as magnetic
compass sensors, the cryptochromes of migratory birds must possess a number of
key biophysical characteristics. Most importantly, absorption of blue light
must produce radical pairs with lifetimes longer than about a microsecond.
Cryptochrome 1a (gwCry1a) and the photolyase-homology-region of Cry1
(gwCry1-PHR) from the migratory garden warbler were recombinantly expressed
and purified from a baculovirus/Sf9 cell expression system. Transient
absorption measurements show that these flavoproteins are indeed excited by
light in the blue spectral range leading to the formation of radicals with
millisecond lifetimes. These biophysical characteristics suggest that gwCry1a
is ideally suited as a primary light-mediated, radical-pair-based magnetic
compass recepto
Pollutant Transport to Subsurface and Surface Waters in an Integrated Farm Operation: PLUARG Special Study No. 22, Report for the period 1975-1977
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